1. Field of the Invention
The invention relates to a socket having contactors that are resiliently pushed to lead pins of a given electrical part mounted, particularly a semiconductor chip with an integrated circuit assembled thereon (hereinafter abbreviated "IC") to establish electrical connections. An example of such socket is the IC chip socket used in the IC chip tester.
2. Description of the Prior Art
In the conventional test of an IC chip, for example, in the heat resistance test in a heating furnace, the IC chip is fitted into a socket 1 as shown in FIG. 1. The body 7 of this socket 1 defines a recessed housing space 5 for housing the IC chip (not shown) where a number of pin contactor 4 (contacts) are disposed on lateral sides of the space 5. To the above socket body 7, a cover 11 and latch 13 are rotatably attached through shafts 10 and 12, respectively. In this construction, the cover 11 is turned in the sense of arrow 14 to fit to the body 7, and the latch 13 is turned in the sense of arrow 15 to hook a locking pawl 17 on an edge 11a of cover 11 for locking.
However, the above socket 1, which is constructed so that the cover 11 may be held in position by the latch 13, has the following weak points:
(1) It is very difficult to open and close the cover 11 when the socket is used on an automatic system;
(2) The leads from the IC chip are fully covered with the cover 11, so that it is difficult to check these legs by eyes for positive contact to individual contactors 4; and
(3) It is unavoidable to design the socket body 7 considerably large in comparison to the IC chip.
These problems are partially solved with a socket 21 of FIG. 2. This socket 21 is equipped with a number of pin contactors 4 in such an array that an IC chip 2 is mounted into the housing space 5 from above these contactors around the chip 2 to touch J-shaped lead pins 3 thereon to lead to a given test circuit (not shown). To describe the above mounting mechanism in more detail, first, each contactor 4 is composed of a fixed base, which has lead legs 6 fitted into holes in the socket body 7 with the lower portion thereof exposed below, and a somewhat outwardly bent resilient section 8 extending from the above fixed base. At the top end of the above section 8, there are provided both a pushing member 9 of short height that is pressed to a pin on the IC chip 2 by a resilient force exerted by the above bent section 8 to nippingly hold the chip and a trigger portion 16 that is disposed almost at the same level as the pushing member 9 and held down by a bottom end face 31a of the cover 31. It is noted that this cover 31 may be so designed as to be put onto the body 7 from above and secured thereto by a locking pawl (not shown). On the other hand, the lead legs 6 are inserted into lead throughholes in a printed circuit board (not shown) and soldered. According to the above construction of socket 21, as the cover 31 is held down, the bottom end face 31a thereof pushes the trigger portions 16 of individual contactors 4 to elastically deform these contactors 4 themselves as illustrated by interrupted lines. Since the above deformation occurs in the outward direction toward lateral walls of the housing space 5, an IC chip 2 can be readily inserted from the position indicated by dot-bar lines to the one indicated by interrupted lines. As the cover 31 is released from the force applied, the contactors 4 attempt to restore the original configuration thereof, when a righting force appears to push the pushing members 9 of contactors 4 against the lateral sides of IC chip 2 so these members may nippingly hold the IC chip 2 in the socket 1. As the pushing members 9 are thus brought in resilient contact to the J-shaped pins 3 of IC chip 2, the chip is electrically connected to a given test circuit through these contactors 4. It is noted that the IC chip 2 can readily be removed by holding down the cover 31 again to resiliently deform the contactors 4 as shown by interrupted lines.
However, the above socket 21 has still the following fatal defects:
(1) The bent sections 8 of contactors 4 are short and bent at a small curvature, so a rather large force must be applied to the cover 31 in order to effectively push down the trigger portions of these contactors. This means a more effort in mounting the IC chip 2.
(2) Further, only the elastic righting force that appears when the bent section 8 attempts to restore the original configuration, namely, the position to hold IC chip 2 as shown by the solid lines from the position of elastic deformation as shown by the interrupted lines determines the holding force exerted by the pushing member 9 to the IC chip 2. Accordingly, lowering the force to be applied to the IC chip 2 for insertion thereof means that the pushing force exerted by the pushing member to the IC chip 2, namely, the nippingly holding force is not satisfactorily high.
(3) Particularly, the larger the number of pins on the socket, the higher the force to operate (and particularly hold down) the cover 31. For this reason, the requirement of low operating force limits the number of pins available on the socket.